I would test the water at school. There is an "acceptable" level of lead in drinking water that isn't zero, and tests of the water system are done statistically at various locations. There could be elevated lead levels in the school's water and it just hasn't been tested. Lots of places are having problems lately, not just Flint.
http://www.post-gazette.com/local/city/2017/01/20/Water-tests-find-lead-again/stories/201701200101